Use of 74HC595 in C51

/* 

Name: Use of 74HC595 

Description: 74HC595 is an 8-bit serial input and parallel output shift register: the parallel output is a three-state output. On the rising edge of SCK, the serial data is input from SDL to the internal 8-bit shift register and output by Q7', while the parallel output is stored in the 8-bit parallel output register at the rising edge of LCK. When the control signal of the serial data input terminal OE is low enable, the output value of the parallel output terminal is equal to the value stored in the parallel output register. When OE is high, that is, the output is turned off, the parallel output terminal will remain in a high impedance state.

One thing to note here is that when the chip needs to generate a rising edge or a falling edge: in essence, it converts the corresponding pin into a high or low level. Of course, it needs to be maintained for a certain period of time as needed (you can use an empty instruction).

For specific pins and instructions, see: Baidu Baike 

(https://baike.baidu.com/item/74HC595/9886491?fr=aladdin)

*/

//Send serial data to HC595

void HC595SendData(unsigned char SendVal)

{  

  unsigned char i;

  for(i=0;i<8;i++) 

   {

        if((SendVal<

            else Out=0; // If true Out= 1  

        //Generate data shift signal

        S_CLK=0;  

        //delay_ms(1);

        NOP(); //Short delay to generate a pulse signal of a certain width

        NOP(); // short delay

        S_CLK=1;

   }

 //Generate data output signal

  R_CLK=0; //set dataline low

        //delay_ms(1);

  NOP(); // short delay

  NOP(); // short delay

    NOP();

  R_CLK=1; //

}

//IO defined in the header file

sbit Out =P3^4; //Serial data line

sbit R_CLK =P3^5; //Data parallel output control

sbit S_CLK =P3^6; //Serial clock line

#define NOP() _nop_() /* define a null instruction*/